1. Field of the Invention
The present invention relates to a transmitting/receiving device, a wireless terminal device and a wireless communication method for sharing a part of frequencies in a complex system including plural communication systems.
2. Description of the Related Art
Conventionally, a study has been made about a method of secondary use of a frequency band of TVWS (TV White Space) using sensing. In the secondary use of a frequency band used in broadcasting, there exists a wide not-used area of the frequency band and it has enough usage value even in a frequency sharing method of comparatively low accuracy. Meanwhile, in secondary use of a frequency band between cellular systems, the area is developed closely in an interfered system (system that suffers from interference) and the not-used frequency area is not broad. Therefore, it is necessary to provide a frequency use method of higher accuracy.
As a method of commonly using a part of frequencies in a complex system including an interfered system (primary system or system that suffers from interference) and an interfering system (secondary system, system that inflicts interference on others), there is known a method in which the interfering system uses a shared frequency band in accordance with presence or absence of a signal of the interfered system in the shared frequency band (see Japanese Patent Application Laid-Open No. 2006-222665). In this method of sharing a frequency band, estimation is done whether or not a signal component of the interfered system is contained in a received signal sensed by the interfering system, and if the received signal does not contain the signal component of the interfered system, the shared frequency band is used in transmission thereby to reduce interference on the interfered system.
However, in the method of sharing a frequency band in the complex system disclosed in JP2006-222665, it is difficult to estimate a signal component of the interfered system accurately due to intra-system interference of the interfering system. In this case, the intra-system interference in a sensing period can be suppressed by issuing a directive to prohibit transmission processing to each terminal in the interfering system before the sensing period. However, if the transmission processing of each terminal is started before issuance of the directive immediately before the sensing period, the terminal cannot be notified of the directive and the intra-system interference in the sensing period cannot be suppressed.